Commitments and Contingencies - Schedule of Accruals for Environmental Matters (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Total Accrual For Environmental Loss Contingencies [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	$ 425	$ 429
Total Accrual For Environmental Loss Contingencies [Member] | Exelon Generation Co L L C [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	71	72
Total Accrual For Environmental Loss Contingencies [Member] | Commonwealth Edison Co [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	288	292
Total Accrual For Environmental Loss Contingencies [Member] | PECO Energy Co [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	33	33
Total Accrual For Environmental Loss Contingencies [Member] | Baltimore Gas and Electric Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	4	2
Total Accrual For Environmental Loss Contingencies [Member] | PEPCO Holdings Inc [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	29	30
Total Accrual For Environmental Loss Contingencies [Member] | Potomac Electric Power Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	26	27
Total Accrual For Environmental Loss Contingencies [Member] | Delmarva Power and Light Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	2	2
Total Accrual For Environmental Loss Contingencies [Member] | Atlantic City Electric Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	1	1
Accrual For MGP Investigation And Remediation [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	319	325
Accrual For MGP Investigation And Remediation [Member] | Exelon Generation Co L L C [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	0	0
Accrual For MGP Investigation And Remediation [Member] | Commonwealth Edison Co [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	286	291
Accrual For MGP Investigation And Remediation [Member] | PECO Energy Co [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	31	31
Accrual For MGP Investigation And Remediation [Member] | Baltimore Gas and Electric Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	2	2
Accrual For MGP Investigation And Remediation [Member] | PEPCO Holdings Inc [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	0	1
Accrual For MGP Investigation And Remediation [Member] | Potomac Electric Power Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	0	0
Accrual For MGP Investigation And Remediation [Member] | Delmarva Power and Light Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	0	1
Accrual For MGP Investigation And Remediation [Member] | Atlantic City Electric Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	$ 0	$ 0